1. Field of the Invention
Aspects of this invention relate generally to air compression systems, and more particularly to a combination compressor and vacuum pump apparatus and method of use.
2. Description of Related Art
The following art defines the present state of this field in connection with compressors generally:
Great Britain Patent No. GB 1043195 to Grant describes a reciprocating piston compressor or air motor having a plurality e.g. four cylinders extending radially from an axial valve chamber housing four angularly spaced ports and in which is rotatably mounted an axially adjustable tubular cylindrical distributing valve provided in a central portion with a suction port and a delivery port and adapted to be brought into sequential communication with each valve chamber port, the outer surface of the valve body is provided with a groove which at or immediately prior to opening of delivery port serves to connect the valve chamber port to an annular chamber bounded in part by the drive end of the valve body and the pressure therein acts against the discharge pressure in an annular chamber at the other end of said valve body and the resulting axial displacement of the valve controls the time of opening of the valve ports according to whether the pressure in one chamber is below or above that in another chamber. The valve portion comprises concentric tubes connected by webs and through which the suction port extends whilst the delivery port extends through the outer tube only. An axial extension tube provides air inlet means to said suction port. Each of the four valve chamber ports are roughly triangular and have a side parallel to the valve axis, a side normal to the axis and the third side has two portions of differing slopes which register with portions of the leading edge of the inlet port and with the leading edge of the delivery port. Lubricant is admitted to a bore leading to grooves and cooling water admitted through a pipe traverses a jacket surrounding the valve and a space round each cylinder. The pistons are each secured to a cross-head connected together in diametrically opposed pairs by the outside member whilst adjacent pistons are connected by connecting members and the cross-heads are reciprocated by two eccentric rings each rotatable within a slide block and having secured thereto a dished disc. The latter are secured together at their peripheries by bars and have balancing weights.
Great Britain Patent No. GB 1259755 to Sulzer Brothers Ltd. describes a compressor wherein a piston reciprocates in a cylinder without normally making physical contact with the cylinder, the piston being provided with a split ring having longitudinal grooves in its periphery. The ring may be of P.T.F.E. and acts to guide the piston in the event of abnormal operation causing the piston to approach the cylinder. During normal operation gas escaping past labyrinth seals or labyrinths formed in the periphery of the piston, acts on a conical ring to centre the piston. Radial holes pass through the ring and open into the grooves thereby to provide pressure equalization between the inside and outside of the ring. The piston may be double or, as shown, single acting and driven by a piston rod which extends through a cylinder seal for connection to a cross-head.
U.S. Pat. No. 4,373,876 to Nemoto describes a compressor having a pair of parallel, double-headed pistons reciprocally mounted in respective cylinder chambers in a compressor housing. The pistons are mounted on a crankshaft via Scotch-yoke-type sliders slidably engaged in the respective pistons for reciprocating movement in a direction normal to the piston axis. The sliders convert the rotation of the crankshaft into linear reciprocation of the pistons. The dimensions of these sliders are determined in relation to the other parts of the compressor so that, during the assemblage of the compressor, the sliders may be mounted in position by being passed over the opposite end portions of the crankshaft following the mounting of the pistons and crankshaft within the housing.
U.S. Pat. No. 5,050,892 to Kawai, et al. describes a piston for a compressor comprising a ring groove on the outer circumferential surface of the piston, and a discontinuous ring seal member with opposite split ends made of a plastic material and fitted in the ring groove. The ring member having an outer surface comprising a main sealing portion having an axially uniform shape and an outwardly circumferentially projecting flexible lip portion. Also, the inner surface of the ring member comprises an inner bearing portion able to come into contact with a first portion of a bottom surface of the ring groove such that the flexible lip portion of the outer surface is brought into contact with a cylinder wall of the cylinder bore and preflexed inwardly. An inner pressure receiving portion is formed adjacent to the inner bearing portion to receive pressure from the compression chamber, to further flex the flexible lip portion upon a compression stroke of the compressor and thereby allow the ring member to expand and the main sealing portion to come into contact with the cylinder wall of the cylinder bore.
Japanese Patent Application Publication No. JP 1985/0079585 to Michio, et al. describes a displacer rod bearing body, provided at its upper and lower parts with rod pin mounting parts, and reciprocatively slides a displacer rod bearing surface around a cross rod pin of a cross head. A displacer rod, secured to a displacer, is rotatably supported to an upper rod pin of the bearing body, and a compressor for the displacer is rotatably supported to a lower rod pin.
U.S. Pat. No. 5,467,687 to Habegger describes a piston compressor having at least one cylinder and a piston guided therein in a contact-free manner, which is connected via a piston rod to a crosshead. The piston rod consists of a pipe extending between the crosshead and the piston. In this pipe extends a tension rod, which can be extended by means of a hydraulic stretching device and under prestressing pulls the crosshead and the piston towards the pipe.
U.S. Pat. No. 6,132,181 to McCabe describes a windmill having a plurality of radially extending blades, each being an aerodynamic-shaped airfoil having a cross-section which is essentially an inverted pan-shape with an intermediate section, a leading edge into the wind, and a trailing edge which has a flange doubled back toward the leading edge and an end cap. The blade is of substantial uniform thickness. An air compressor and generator are driven by the windmill. The compressor is connected to a storage tank which is connected to the intake of a second compressor.
U.S. Patent Application Publication No. US 2002/0061251 to McCabe describes a windmill compressor apparatus having multiple double acting piston/cylinders actuated by the windmill. The windmill additionally has multiple pairs of blades to enhance power output and lift.
U.S. Pat. No. 6,655,935 to Bennitt, et al. describes a gas compressor and method according to which a plurality of inlet valve assemblies are angularly spaced around a bore. A piston reciprocates in the bore to draw the fluid from the valve assemblies during movement of the piston unit in one direction and compress the fluid during movement of the piston unit in the other direction and the valve assemblies prevent fluid flow from the bore to the valve assemblies during the movement of the piston in the other direction. A discharge valve is associated with the piston to permit the discharge of the compressed fluid from the bore.
U.S. Pat. No. 6,776,589 to Tomell et al. describes a reciprocating piston compressor having a suction muffler and a pair of discharge mufflers to attenuate noise created by the primary pumping frequency in the primary pumping pulse. The suction muffler is disposed along a suction tube extending between the motor cap and the cylinder head of the compressor. The discharge mufflers are positioned in series within the compressor to receive discharge gases from the compression mechanism and are spaced one quarter of a wavelength from each other so as to sequentially diminish the problematic or noisy frequencies created during compressor operation. The motor/compressor assembly including the motor and compression mechanism is mounted to the interior surface of the compressor housing by spring mounts. These mounted are secured to the housing to define the position of the nodes and anti-nodes of the frequency created in the housing to reduce noise produced by natural frequencies during compressor operation.
In connection with combination compressor and vacuum pump units, more particularly, a typical application of such technology is in connection with an oxygen concentrator or oxygen generator, a device used to provide oxygen therapy to a patient at substantially higher concentrations than those of ambient air and so employed as an alternative to tanks of compressed oxygen. Oxygen concentrators may also provide an economical source of oxygen in industrial processes. The typical oxygen concentrator works off of the principle of Pressure Swing Adsorption (PSA). A PSA concentrator is capable of continuous delivery of oxygen and has internal functions based around two cylinders, or beds, filled with a zeolite material, which selectively adsorb the nitrogen in the air. In each cycle, air is flowed through one cylinder at a pressure of around 20 lbf/in2 (138 kPa or 1.36 atmospheres) where the nitrogen molecules are captured by the zeolite, while the other cylinder is vented off to ambient atmospheric pressure allowing the captured nitrogen to dissipate. Such units typically have cycles of around 20 seconds and allow for a continuous supply of oxygen at a flow rate of up to approximately five liters per minute (LPM) at concentrations anywhere from 50 to 95%. A similar prior art process is known as Vacuum Swing Adsorption (VSA), which uses a single low pressure blower and a valve which reverses the flow through the blower so that the regeneration phase occurs under a vacuum. A still further alternative prior art approach to oxygen concentration employs technology known as Advanced Technology Fractionator (ATF). A rotary distribution valve built into the ATF directs the flow of compressed air to a group of four molecular sieve beds at any given time. Simultaneously, another four beds are allowed to purge to atmosphere through the rotary valve. The remaining four beds are interconnected through the valve to equalize pressure as they transition between adsorbing and desorbing. The combined twelve sieve beds of the ATF device contain about the same amount of molecular sieve as the conventional two-bed oxygen concentrator. In any of the above approaches, a compressor or a combination compressor and vacuum pump may be employed in pressurizing, delivering, and/or purging air within the system as the concentrator operates. A typical such compressor and vacuum pump unit is manufactured and sold by Rietschle Thomas. For example, the WOB-L® Piston design Model 2250 employs a rocker piston arrangement driven by a brushless DC motor offering variable speed from 1,000 to 3,000 RPM, whereby the air flow of the concentrator can be varied according to patient need. In addition, an optional closed loop controller may allow motor speed to be maintained at a pre-set, constant RPM regardless of load or voltage fluctuations. The oil-less piston and cylinder design reduces contaminants in the air flow, and the use of magnesium components minimizes the pump's weight, important features for portable oxygen concentrators.
The prior art described above teaches single and double-acting air cylinders, and specifically combination compressor and vacuum units for use in connection with oxygen concentrators, but does not teach introducing air into or discharging air from an air cylinder through a hollow piston rod or the use of a piston-cylinder arrangement having relatively long-stroke, slow movement to achieve the required pressures and flow rates more efficiently and quietly and with less heat build-up and wear. Aspects of the present invention fulfill these needs and provide further related advantages as described in the following summary.